Tanker-trailers of the type which transport cargo often require that the cargo be maintained at a predetermined temperature. This does not present a problem for the carrier during the actual travel time spent with the cargo, as the trailer is equipped with a temperature control system which operates off the heating system of the tractor.
During stop-overs, however, and those times when the trailer is disconnected from the tractor, the temperature maintenance noted above is not possible unless the tractor is maintained in contact with the trailer. This can result, in those cases where the cargo is a perishable food, in food spoilage. And in those cases where the tractor and trailer hook-up is maintained, just to provide for temperature control, an inefficient condition is created since the tractor is being used for a purpose for which it was not intended when it could be used for its intended purpose of transporting.
It would, therefore, be desirable to have a way of maintaining the desired predetermined temperatures for the trailer and its cargo without having to use a tractor during the noted stop-overs.